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Breaking Habits

Whether it's biting your nails, chewing on a pen or watching too much TV, everyone has a habit and they are very hard to break. Watch as Duke scientists explore the lasting changes habits leave on the circuitry of our brains.

DURHAM — So there you are again, working at your desk, or watching television; maybe reading a book. In one hand you have the remote, and in the other? A snack.

You find yourself eating, even though you are not hungry. Have you ever wondered why this happens?

Or have you ever stopped to wonder why you turn on the light switch as soon as you step into a dark room, without giving it a second thought? What about why you left work and found yourself parking the car at your house, without remembering the drive home?

These activities have all become habits. Habits are defined as an acquired behavior pattern regularly followed until it has become almost involuntary. Essentially, it’s something you do so often that eventually you are not even conscious about doing it.

“Habits aren’t just there, but you get them by repetition and reinforcement,” explains Dr. Nicole Calakos, M.D., Ph.D. and associate professor of neurology and neurobiology at the Duke University Medical Center. "The repetition part is obvious, because a habit means regularly doing something, and the more you do it, the conditions are ripe that will make you prone to have a habit. The second is reinforcement. In other words, is the outcome good? Does it help you get about your business? Is it rewarding? And things like that.”

Now, there is new insight on habits, how we form them and why it’s tough to change them. Duke University researchers have discovered that habits—good or bad—leave a lasting mark on specific circuits in the brain. That’s right, habits actually change the wiring in your brain.

“Habits actually help us survive,” says Justin O’Hare, a neurobiology graduate student at Duke. “Imagine in your day-to-day life, [with] every tiny, mundane thing you do, you really had to think about the cause and effect. You’d have to stop and rationalize, 'I need this, so I need to think about a solution.' It would be really crippling and it would make it impossible to do things that really need a lot of attention.”

The Duke team used mice to study the development of habits. They enabled the mice to form sugar habits, with a process that required the mice to press a lever to get a treat. The mice were put into a special holding pen once a day, for an hour a day, for one week.

Some of the mice had clearly formed a habit when the animals kept pressing the lever even after the treats were removed.

“We could see that some of the mice were goal-oriented, and they pushed the lever and when nothing came out they moved on,” says Dr. Calakos. “But you could tell that some of the mice had developed a disconnect with the sugar pellet and they just kept pressing the lever. For them, the lever pushing was habitual.”

Researchers then compared the brains of the mice that had formed a habit to the ones that didn’t. They paid special attention to the electrical activity in the basal ganglia. It’s a part of the brain that controls motor actions and compulsive behavior.

The basal ganglia is found deep inside the brain. The section of the brain has two main pathways, which carry opposing messages. One pathway carries a go signal, which encourages an action. The other pathway, as you might guess, is a stop signal.

The researchers found that, in the mice that had formed a habit, the cells in both the stop and go pathways were equally active.

Post-graduate researcher Kristen Ade used a two-photon microscope to study the pathways side-by-side under the same experimental conditions to compare the activity.

“We found that all of the cells fired more in the habit trained mice,” explains Ade, pointing to a computer image of the cells in a slice of the basal ganglia. “But then we also found the yellow or red dyed cells firing more than the green cells in the habit trained mice.”

Ultimately, they all were being fired.

“It was a little surprising that all of the cells were active because we were thinking there was a little cluster of lever pressing cells, and not this whole brain region,” says Dr. Calakos. “But that gives us a clue about how the brain encodes information, that habit is this diffuse layer that coats the whole cell.”

In addition, the team found that the go pathway turned on before the stop pathway in mice that had formed habits. For the non-habit oriented brains, the stop signal fired first.

“And this is kind of cool, because instead of just the responses getting everything fired up, they seemed to be in a race,” adds Dr. Calakos, who describes this finding as even more surprising than the first. “The timing of what brain cell fired first predicted whether mouse was habitual or not. In a habit mouse, the green light cells fired first, while in the non-habit mouse, the timing flipped flopped and the stop sign fired just before.”

The research also begs the question of how you would stop a bad habit. To find out, the Duke team tried to change the habits of the mice. The mice, which had been rewarded for pressing the lever were then rewarded only when they stopped pressing it. In short, they found the wired brain had to be rewired.

“We did see what it was like to break a habit, and it’s clear the formative process is not the same as breaking a habit,” explains Dr. Calakos. “Successfully breaking a habit was predicted by one change in the circuitry. And that was if the green light cells quieted down.”

For the green light or go pathway cells to be quieted in the mice that had developed a habit, the mice had to make a conscious decision to stop pushing the lever, in order to reap the rewards.

Researchers are still working on how that information relates to humans with bad habits. But the research suggests breaking a habit isn’t easy, or done quickly.It also takes the conscious rethinking of an action.

“If you could dampen the go signal, that predicted whether you would successfully break the habit,” says Dr. Calakos. “So we have the language here of this is what it’s like to make a habit and this is what it’s like to break a habit.”

While some everyday habits, like flipping a light switch, or driving a car, are important to have, other habits, we might want to break. And while it might be hard to rewire our brains to think differently, the research from Duke has shown us that it is possible. It might just take some conscious effort.